The present invention relates to plural component spray guns, and in particular to a device for purging residual mixed components from a mixing chamber and an airless fluid tip of a plural component airless spray gun.
The purging device of this invention finds use in plural component plastic application equipment or guns of the general type described and claimed in U.S. Pat. No. 3,366,337, issued Jan. 30, 1968, wherein two coreactive streams of chemicals are intimately mixed within the gun and dispensed from an airless tip in a spray.
One problem which arises in prior art plural component guns is that, between operations, the residual material in the mixing chamber and/or in the outlet nozzle tends to harden, thereby making further mixing and dispensing impossible until the chamber and nozzle are purged of the hardened residue. In the aforementioned U.S. Pat. No. 3,366,337, purging is accomplished by manually opening a needle valve to admit a flow of solvent and/or air through the chamber and nozzle to remove the residue. This purging procedure, however, has several disadvantages. First, the use of solvent adds unnecessary expense to the spraying process. Second, because of being ejected under pressure, the solvent is dispersed into the surrounding air and creates potential safety and environmental health problems. Further, the blast of solvent and/or air, while forcefully ejecting hardened residue, scatters the residue haphazardly. Overall, this cleaning arrangement is unsatisfactory.
Other prior art arrangements utilize a rod to eject excess material, such as for example in Henderson U.S. Pat. No. 4,133,483. The gun there described is for mixing and dispensing plural component plastic materials, and the rod that performs the purging process is normally positioned rearwardly of both the mixing chamber and of reactive component inlet orifices to the chamber, and is selectively movable forwardly through the chamber to purge the chamber of residual material. The gun has a circular fluid outlet orifice from the mixing chamber and does not utilize either pneumatics or hydraulics to atomize emitted materials; rather, the mixed components "pour" out of the gun.